The present invention relates to a composition which comprises at least one triblock copolymer, one terpene resin, one liquid component and one ethylene-vinyl acetate copolymer, and also to a process for preparing this composition, to its use and to a multilayer product comprising the composition of the invention.
The adhesives industry is looking for adhesives which adhere not only to polar articles but in particular to apolar articles as well.
U.S. Pat. No. 4,412,030 discloses hotmelt pressure-sensitive adhesives (hmPSAs) which are composed of a special resin based on phenyl and styrene and/or α-methyl styrene, a triblock diene copolymer and an ethylene-vinyl acetate copolymer. The latter has vinyl acetate contents of up to a maximium of 45% by weight.
EP-A 0 934 990 discloses a hotmelt adhesive composition and its use for bonding paper at 121° C. Among its constituents the claimed composition includes an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by weight and a melt flow index (“MFI”) of 1000. For the use of this composition on all substrates and articles, the temperature range is unsuitable.
Pressure-sensitive adhesive (PSA) compositions for polyolefin surfaces are disclosed in EP-A 0 822 967. They comprise solution-polymerized acrylates with chlorinated polyolefins and hydrocarbon tackifiers.
U.S. Pat. No. 4,357,459 describes a styrene resin which is modified by Friedel-Crafts reaction and which can be reacted together with acrylates or ethylene-vinyl acetate copolymers as a hotmelt adhesive (hm) or as a pressure-sensitive adhesive (PSA). Ethylene-vinyl acetates having a low vinyl acetate content are used.
JP-A 2000 142 650 mentions a hotmelt adhesive (hma) which is based on ethylene-vinyl acetate copolymers and is applied to moving objects at 70° C.
The adhesive composition in JP-A 2000 137 438 is based on an ethylene-vinyl acetate copolymer prepared so as to be detachable from glass surfaces.
WO 00/27942 describes a paper label comprising ethylene-vinyl acetate copolymer in an adhesive bond. This bond is generally unsuitable for very smooth surfaces such as plastics.
In product information literature from Kuraray (LIR Technical Information 1998,9 (1,000), p. 20, Kuraray Europe GmbH, Schiess-Strasse 68, 40549 Dusseldorf, Germany) hotmelt adhesive mixtures are disclosed which differ from the present invention only in the vinyl acetate content of the ethylene-vinyl acetate copolymers used. The product with an increased vinyl acetate content of 40% by weight shows no increase in tack over a vinyl acetate content of 28% by weight. For the product with the increased vinyl acetate content it is possible to observe poorer adhesion to PE than for the product with the lower vinyl acetate content.
The state of the art presents a variety of adhesives which are tailored to the particular material on which they are used but which do not adhere to smooth, relatively polar and also apolar surfaces of thermoplastics.
The object of the present invention is, therefore, to provide a composition which adheres both to polar and to apolar surfaces of thermoplastics and which allows an adhesive for thermoplastic surfaces to be provided.